Buffer Status Reporting in Small Cell Networks

ABSTRACT

A wireless communication method wherein: a terminal ( 1 ) transmits first and second data streams to a network; wherein the first data stream is associated with both a first cell and a second cell of a plurality of cells ( 10, 20, 22, 24 ) serving the terminal, and the second data stream is associated with the second cell; and the terminal ( 1 ) transmits at least one signalling message including first information relating to data to be sent in the first data stream and/or second information relating to data to be sent in the second data stream to at least one of the first cell and the second cell based on predetermined rules corresponding to association between cells and data streams.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/984,606, filed Dec. 30, 2015, which is a continuation of ApplicationPCT/EP2014/053713, filed Feb. 26, 2014, which claims priority from theEuropean Patent Application No. 13176091.0, filed Jul. 11, 2013, thecontents of each are herein wholly incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to cellular wireless networks,particularly to so-called Small Cell networks and more particularly tothe transmission by terminals of scheduling requests in such networks.

BACKGROUND OF THE INVENTION

Cellular wireless networks are widely known in which base stations (BSs)communicate with terminals (also called user equipments (UEs), orsubscriber or mobile stations) within range of the BSs. The geographicalareas covered by base stations are generally referred to as cells, andtypically many BSs are provided in appropriate locations so as to form anetwork or system covering a wide geographical area more or lessseamlessly with adjacent and/or overlapping cells. (In thisspecification, the terms “system” and “network” are used synonymouslyexcept where the context requires otherwise). In each cell, theavailable bandwidth is divided into individual resource allocations forthe user equipments which it serves. Communications in the networkcomprise downlink communications from the base station to the terminal,and uplink communications from the terminal to the base station. Data tobe transmitted in the uplink, in the form of a data stream comprising asequence of data packets, may be user data or control data and may havedifferent QoS (Quality of Service) requirements, depending on theapplication or purpose.

Basic LTE Network

One type of cellular wireless network is based upon the set of standardsreferred to as Long-Term Evolution (LTE). The current version of thestandard, Release 11, is also referred to as LTE-A (LTE-Advanced). Thenetwork topology in LTE is illustrated in FIG. 1. As can be seen, eachterminal 1, called a UE in LTE, connects over a wireless link via a Uuinterface to a base station in the form of an enhanced node-B or eNodeB11. It should be noted that various types of eNodeB are possible. AneNodeB may support one or more cells at different carrier frequencieshaving differing transmit powers and different antenna configurations,and therefore providing coverage areas (cells) of differing sizes.Multiple eNodeBs deployed in a given geographical area constitute awireless network called the E-UTRAN (and henceforth generally referredto simply as “the network”). Cells in an LTE network can operate eitherin a Time Division Duplex, TDD, mode in which the uplink and downlinkare separated in time but use the same carrier frequency, or FrequencyDivision Duplex, FDD, in which the uplink and downlink occursimultaneously at different carrier frequencies.

Each eNodeB 11 in turn is connected by a (usually) wired link using aninterface called S1 to higher-level or “core network” entities 101,including a Serving Gateway (S-GW), and a Mobility Management Entity(MME) for managing the system and sending control signalling to othernodes, particularly eNodeBs, in the network. In addition (not shown), aPacket Data Network (PDN) Gateway (P-GW) is present, separately orcombined with the S-GW, to exchange data packets with any packet datanetwork including the Internet. Thus, communication is possible betweenthe LTE network and other networks.

Small Cell Network (SCN) FIG. 1 shows what is sometimes called a“homogeneous network”; that is, a network of base stations in a plannedlayout and which have similar transmit power levels, antenna patterns,receiver noise floors and similar backhaul connectivity to the corenetwork. Current wireless cellular networks are typically deployed ashomogeneous networks using a macro-centric planned process. Thelocations of the base stations are carefully decided by networkplanning, and the base station settings are properly configured tomaximise the coverage and control the interference between basestations. However, it is widely assumed that future cellular wirelessnetworks will adopt a “heterogeneous network” structure composed of twoor more different kinds of cell, also (and henceforth) referred to as aSmall Cell Network or SCN.

FIG. 2 depicts a simple SCN. The large ellipse 10 represents thecoverage area or footprint of a Macro cell provided by a base station(Macro BS) 11. The smaller ellipses 20, 22 and 24 represent Small cellswithin the coverage area of Macro cell 10, each having a respective basestation (exemplified by Pico BS 21). Here, the Macro cell is a cellproviding basic “underlay” coverage in the network of a certain area,and the Small cells are overlaid over the Macro cell, using the same ordifferent carrier frequencies for capacity boosting purposesparticularly within so-called “hot spot zones”. A UE 1 is able tocommunicate both with Macro BS 11 and Pico BS 21 (but not necessarilysimultaneously) as indicated by the arrows in the Figure. When a UEstarts to use a given cell for its communication, that cell is said tobe “activated” for that UE, whether or not the cell is already in use byany other UEs. Incidentally, although the Macro and Small cells aredepicted here as being provided by different base stations, this is notessential and the same base station may be responsible for both a Macrocell and a Small cell. For example, a cell operating in a higherfrequency band is likely to experience greater pathloss, and thus haveshorter range, than one in a lower frequency band; thus the same basestation may provide both a lower-frequency Macro cell and ahigher-frequency Small cell.

Although only two types of cell are shown in FIG. 2, various types ofSmall cell may be present in a SCN including (in decreasing order ofsize), cells similar to current Micro, Pico and Femto cells. Femto andPico cells can be overlaid on either Macro or Micro cells. Thus,networks can be designed such that the Macro cells provide blanketcoverage while the Micro, Pico and/or Femto cells (or Small Cells)provide additional capacity. The envisaged Small Cells may alsocorrespond to a New Carrier Type (NCT) not yet defined in LTEspecifications.

Carrier Aggregation (CA)

SCNs will support and enhance various capacity-boosting schemes to beapplied to UEs, including so-called Carrier Aggregation (CA) which hasbeen introduced into 3GPP (in the homogeneous network context) since LTERelease 10. Details of CA as applied to LTE are given in the 3GPPstandard TS36.300, hereby incorporated by reference.

In CA, two or more Component Carriers (CCs) at different carrierfrequencies are aggregated in order to support wider transmissionbandwidths up to 100 MHz (made up of a maximum of five CCs each having abandwidth around their carrier frequency of up to 20 MHz). A UE maysimultaneously receive or transmit on one or multiple CCs depending onits capabilities.

Management of connections of UEs to the network, broadcast of systeminformation and establishment of radio bearers is part of Radio ResourceControl (RRC). When CA is configured, the UE only has one RRC connectionwith the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides thesystem information which the UE needs to join the network, and this cellis referred to as the Primary Cell (PCell). All other CCs are calledSecondary Cells or SCells. Generally, one carrier corresponds to onecell. In the downlink, the carrier corresponding to the PCell is theDownlink Primary Component Carrier (DL PCC) while in the uplink it isthe Uplink Primary Component Carrier (UL PCC). Incidentally, in thisspecification the terms “carrier” and “cell” are used somewhatinterchangeably; it should be borne in mind, however that althoughdifferent carrier frequencies always imply different cells, the reverseis not necessarily the case: a single carrier frequency can support oneor more cells.

Therefore, a UE using CA has a plurality of serving cells, one for eachCC, and the CCs may for example correspond to Macro and Small cells in aSCN, such that the same UE may use the Macro cell as its “primary” cell(PCell) and a Small cell as a “secondary” cell (SCell). As well aspossibly having different carrier frequencies, the Macro and Small cellsmay have different bandwidths. Generally, each cell is provided by basestation antennas at a single site, but this does not exclude thepossibility of one cell being provided by antennas at different sites.

A potential issue with CA in SCNs is that at least some of the CCs arelikely to be provided by small base stations similar to existing HomeeNodeBs and femtocells, which use broadband internet for their backhaulconnectivity to the network, and are therefore liable to incur greaterlatency (including a greater time taken to exchange information withother base stations) compared with macro cell eNodeBs.

Where the CCs are provided by geographically-separated base stations,these base stations will also generally experience different signalpropagation delays from the UE. In order to take advantage of CA in theSCN scenario, Release 11 of LTE provides for multiple uplink TimingAdvances (TAs), by which a UE can ensure that its uplink transmissionsarrive in synchronization with transmissions from other UEs at the basestations providing the cells. Since the same base station may providemore than one cell, the concept of a Timing Advance Group (TAG) is usedto group together carriers with the same TA value. However, variousaspects of how CA may be most advantageously applied to the SCN have yetto be determined, as explained later.

Uplink Channels in LTE

Since the embodiments to be described concern buffer status reports(BSRs) in SCNs, some further explanation will be given of the nature of,and need for, these status reports.

An LTE system is a scheduled system in which transmission is organizedin “frames” each containing twenty slots, two consecutive slots beingreferred to as a “subframe”. For each transmission time interval of oneor more subframes, a new scheduling decision is taken regarding whichUEs are assigned/allocated to which time/frequency/spatial/coderesources during this transmission time interval.

Several “channels” for data and signalling are defined at various levelsof abstraction within the network. FIG. 3 shows some of the channelsdefined in LTE-based systems at each of a logical level, transport layerlevel and physical layer level, each corresponding to a differentprotocol layer within the well-known OSI model, and the mappings betweenthem. For present purposes, the uplink channels are of particularinterest.

In FIG. 3, physical channels defined in the uplink are a Physical RandomAccess Channel (PRACH), a Physical Uplink Shared Channel (PUSCH), and aPhysical Uplink Control Channel (PUCCH). An uplink physical channelcorresponds to a set of resources carrying information originating fromhigher layers. In addition to the uplink channels, uplink signals suchas reference signals, primary and secondary synchronization signals aretypically defined.

At the transport channel level in FIG. 3, an uplink shared channelUL-SCH maps to the physical channel PUSCH whilst a random access channelRACH maps to the above mentioned PRACH. Incidentally, although FIG. 3shows logical channels, these define set of logical channel types fordifferent kinds of data transfer services as offered by the MAC, whereeach logical channel type is defined by what type of information istransferred. It should be noted that in this invention logical channelsrefer to the logical channels used in the logical channel Prioritisationprocedure in the MAC where the actual logical channels are defined byRRC configuration.

The above mentioned 3GPP TS 36.300 provides an overall description ofthe radio interface protocol architecture used in LTE-based systems andin particular section 5.2 of 3GPP TS 36.300 relates to uplinktransmission schemes. The physical channels in the uplink of LTE-basedsystems are described, for example, in 3GPP TS 36.211, section 5, whichis hereby also incorporated by reference.

User data and optionally also higher-level control signalling is carriedon the Physical Uplink Shared Channel PUSCH. The physical uplink controlchannel PUCCH carries uplink control information such as a schedulingrequest (SR), see below, and a channel quality indicator (CQI) report.As illustrated in FIG. 3, there is a downlink counterpart channel to thePUCCH, which is the Physical Downlink Control Channel (PDCCH) forcarrying, in response to the scheduling request, an uplink schedulinggrant. Incidentally, in LTE-A there is also an enhanced PDCCH calledEPDCCH, which allows coordination among eNodeBs for reducing inter-cellinterference.

The uplink scheduling grant also indicates the transmission rate (i.e.modulation and code rate). If PUSCH transmission occurs when the PUCCHwould otherwise be transmitted, the control information to be carried onPUCCH may be transmitted on PUSCH along with user data. Simultaneoustransmission of PUCCH and PUSCH from the same UE may be supported ifenabled by higher layers. The PUCCH may support multiple formats asindicated in 3GPP TS 36.211, section 5.4.

Because transmissions between UE and base station are prone totransmission errors due to interference, a procedure is available foreach packet sent in uplink and downlink direction to be acknowledged bythe receiver. This is done by sending Hybrid Automatic Repeat Request(HARQ) acknowledgments or non-acknowledgments (ACK/NACK) on controlchannels. On the downlink, ACK/NACK is sent on a Physical HARQ IndicatorChannel (PHICH). On the uplink ACK/NACK is sent on PUCCH.

The Physical Random Access Channel PRACH is used to carry the RandomAccess Channel (RACH) for accessing the network if the UE does not haveany allocated uplink transmission resource. If a scheduling request (SR)is triggered at the UE, for example by arrival of data for transmissionon PUSCH, when no PUSCH resources have been allocated to the UE, the SRis transmitted on a dedicated resource for this purpose. If no suchresources have been allocated to the UE, the RACH procedure on PRACH isinitiated.

Channels in CA

Having outlined some of the more important channels defined in LTE,their relationship to cells/CCs in the CA scenario can now be describedusing FIG. 4.

As shown in FIG. 4, under current LTE proposals, each PCell can transmitPDCCH to a UE. An SCell may (or may not) provide PDCCH to a UE,depending on UE capabilities; however, uplink data on PUSCH, and BSR andsome RACH can be transmitted by a UE having the required capabilities,on both PCell and SCell. Correspondingly there is a separate transportchannel UL-SCH for each cell. For LTE up to and including Release 11 theuplink control channel (PUCCH), which supports SR, is only transmittedon the PCell. Similarly, PRACH for scheduling requests is onlytransmitted on the PCell. However, these restrictions may not apply infuture Releases.

If an SCell does not carry PDCCH, this implies that the schedulinginformation for that cell has to be carried in PDCCH of another cell(typically the PCell)—so called cross-carrier scheduling. The PCell andSCells should have identical or very similar transmission timing whichallows, for example, PDCCH on one cell to schedule resources on adifferent cell, and ACK/NACKs for PDSCH transmissions on SCells to besent on the PCell. SCells may have different transmission timing at theUE in order to allow for the possibility that the cells are supported byantennas at different geographical sites. A PCell and/or SCells with thesame timing would belong to the same TAG (Time Alignment Group).However, because of the tight timing synchronization requirementsbetween PUCCH on the PCell and PDSCH on the SCells, PCells and SCellscan be assumed to be controlled by the same eNodeB.

Radio Bearers and Logical Channels

In an OSI-compliant standard such as for LTE, protocol layers defined inthe system (i.e. E-UTRAN) include Packet Data Control Protocol (PDCP),Radio Link Control (RLC) and Medium Access Control (MAC). FIG. 5 showsthe major uplink functions in the system at each of the PDCP, RLC andMAC protocol layers when employing CA. FIG. 5 shows the case of twocomponent carriers CC1 and CC2, corresponding to a PCell and SCell forexample. With respect to a given node (for example an eNodeB or UE),each protocol can be considered to reside in a functional module or“entity” which can be considered separately from protocols in otherlayers. This allows, among other things, for the use of the concept of“radio bearers”, which provide a kind of tunnel between peer entities inthe eNodeB and UE at a given protocol level for user data or controlsignalling. Establishment and maintenance of radio bearers is anotheraspect of RRC.

Packets belonging to the same radio bearer get the same end-to-endtreatment in the network. A bearer can be characterised by parameterssuch as “Guaranteed Bit Rate” (GBR) and “non-GBR”. For GBR bearers, thenetwork guarantees a certain bit rate to be available for the bearer atany time. The bearers, both GBR and non-GBR are further characterized bya Maximum Bit Rate (MBR), which limits the maximum rate that the networkwill provide for the given bearer. In this way it is possible for eachradio bearer to provide a certain quality of service, QoS appropriate toa data stream carried on the radio bearer.

In LTE/E-UTRAN, the above mentioned radio bearers (RBs) are defined atvarious protocol levels including PDCP. There are three kinds of PDCPbearers: SRB (Signalling Radio Bearer) and two kinds of DRB (DedicatedRadio Bearer), AM DRB and UM DRB where AM stands for Acknowledged ModeRLC and UM for Unacknowledged Mode. In E-UTRAN there are only threeSRBs—SRB0, SRB1 and SRB2. These are used by control plane protocol tosend the packets to the UE. DRBs are used for sending voice and data; asmany DRBs are set up as the number of QoS streams or services requiredby the terminal. When a DRB is set up, a Logical Channel Identity (LCID)will be assigned to this DRB for UL and DL. In this sense, it may besaid that one logical channel (LC) conventionally corresponds to one RB.

For the purpose of resource allocation, the logical channels may in turnbe assigned to Logical Channel Groups (LCGs), LCs of similar QoS demands(QoS Class Identifier, and/or priority (QCI)) being placed in the sameLCG. Each LC is assigned to only one LCG and the assignment of an LC toa LCG may be done on the basis of required quality of service (e.g.priority, delay requirements). The primary motivation for defining LCGsis to reduce the amount of control signalling compared with providingcontrol signalling for each individual LC.

The LC may be assigned to the RB, and LC may be assigned to a LCG, whenthe RB is set up; however it may be useful to reassign LCs to LCGs forexample when a new RB is added or an existing RB is removed.

The MAC layer, apart from managing the above-mentioned hybrid ARQfunction, is responsible for mapping of data between the logicalchannels to transport channels, each of which may carry more than oneLC. Transport channels DL-SCH and UL-SCH represent data transferservices offered by the PHY and are defined by how the information iscarried, different physical layer modulations and the way they areencoded.

A MAC entity of the eNodeB in an LTE system includes a schedulingfunction responsible for managing resource scheduling for both uplinkand downlink channels, that is, to allocate physical layer resources forthe DL-SCH and UL-SCH transport channels. Different schedulers operatefor the DL-SCH and UL-SCH. The scheduler should take account of thetraffic volume (buffer status) and the QoS requirements of each UE andassociated radio bearers, when sharing resources between UEs. Schedulersmay assign resources taking account the radio conditions at the UEidentified through measurements made at the eNodeB and/or reported bythe UE. Likewise, the UE has a MAC entity with a scheduling functionfor, in accordance with a resource allocation signalled to it by theeNodeB, constructing transport blocks from data for transmission whichhas arrived in a buffer of the UE.

In the scenario of CA within LTE, as can be seen from FIG. 5, themulti-carrier nature of the physical layer is only exposed to the MAClayer for which a separate UL-SCH is provided by each CC (serving cell)and one HARQ entity is required per serving cell.

The relationship (mapping) between radio bearers, logical channels/LCGs,and transport channels is summarised in FIG. 8, in which the downwarddirection represents the progression from higher-level to lower-levelprotocol layers.

Thus, at the top of the protocol stack is an application running on theUE, a camera application or Voice over IP (VoIP) for example. Thisgenerates a data stream such as photographs or voice packets to beuploaded to the network. Each data stream has an associated QoSrequirement. In the example of a camera application, a “best effort”service would suffice; on the other hand VoIP would have a morestringent QoS requirement to minimise latency. The data stream maps to aradio bearer (DRB) which in turn corresponds to a logical channel. Thus,a data stream may be mapped to one logical channel (although LTEspecifications do not prevent mapping a data stream to more than onelogical channel), and the logical channel may be assigned to a logicalchannel group. Transport channels are constructed from the logicalchannels and transmitted on the uplink physical channels.

Buffer Status Report (BSR) and Scheduling Request (SR)

Based on the current 3GPP standard as set out in TS36.300, measurementreports, including transport volume and measurements of a UE's radioenvironment, are required to enable the scheduler in the eNodeB tooperate in both uplink and downlink. Especially, in the uplinkdirection, uplink buffer status reports (BSR), including information onbuffer status for different logical channels, are needed from the UEs toprovide support for QoS-aware packet scheduling by the eNodeB.

That is, in order to schedule uplink transmissions efficiently thenetwork needs to be aware of the amount (volume) of data that the UEneeds to transmit, the priority of such data (in the form of datastreams of different types and priorities, reflecting different servicesbeing provided to the UE), and the uplink channel conditions. In LTEspecifications this is provided for by the UE sending BSRs (bufferstatus reports) along with data transmissions via PUSCH, and bytransmission of UL sounding reference signals (SRS).

A BSR indicates the amounts of data buffered at the UE (i.e., ready fortransmission on the uplink) with respect to either one or four LogicalChannel Groups. In LTE the LCGs are processed with different priorities.Thus, the concept of LCGs allows the BSR to provide information on dataamounts categorised by priority. Four LCGs and two formats are used forreporting in the uplink:

-   -   A short format for which only the buffer status of one LCG is        reported;    -   A long format for which buffer statuses of all four LCGs are        reported.

The short format is shown in FIG. 6 and the long format is shown in FIG.7. As indicated in FIG. 6, one specific LCG identified by the firstfield “LCG ID”, the amount of data being signified by the second field,“Buffer Size”. In the long format BSR shown in FIG. 7, it will be notedthat explicit LCG IDs are not used, the LCG concerned being implicitfrom the relative position of the Buffer Size field within the report.If not all four LCGs are configured then the UE simply reports “0”(zero) for the status of any non-configured LCG.

However, if the UE has no PUSCH resources available, there is no meansto send a BSR. In such cases a scheduling request (SR) is triggered inthe UE. The SR indicates that the UE needs to be granted UL resources onPUSCH. In some cases the UE may not have an SR resource allocation onPUCCH, and then the RACH procedure is initiated as already mentioned. ABSR supersedes the SR in the sense that when a SR is triggered, it isconsidered as pending until it is cancelled by transmission of a BSRwhich contains buffer status up to (and including) the last event thattriggered a BSR, or when the UL grant(s) can accommodate all pendingdata available for transmission.

The BSR and SR protocols are further described in 3GPP TS 36.321,sections 5.4.4, 5.4.5, and 6.1.3, and the SR procedure for a terminalprocedure for determining physical uplink control channel assignment isdescribed in 3GPP TS 36.213, section 10, which is also herebyincorporated by reference.

To summarise the foregoing, currently in LTE buffer status reports areused to indicate to the network information about the data ready to betransmitted from the terminal in the uplink. Data streams correspondingto logical channels are associated with logical channel groups, anddepending on the arrival and priority of new data, a buffer statusreport (BSR) may be triggered. If no (PUSCH) resources are available tocarry a BSR, a scheduling request (SR) may be transmitted. If noresources for SR are allocated, then a random access (RACH) transmissionmay take place. In the 3GPP specifications a data stream may beconsidered to correspond to a radio bearer, which would include bothsignalling radio bearers (SRB) and data radio bearers (DRB).

In Carrier Aggregation (CA), in addition to the PCell one or more SCellsat different carrier frequencies may be configured for a UE. The PCelland SCells should have identical or very similar transmission timing,which allows, for example, PDCCH on one cell to schedule resources on adifferent cell, and ACK/NACKs for PDSCH transmissions on SCells to besent on the PCell. Uplink transmissions from the UE via each SCell mayhave different transmission timings at the UE in order to allow for thepossibility that the cells are supported by antennas at differentgeographical sites. A PCell and/or SCells with the same timing wouldbelong to the same TAG (Time Alignment Group). However, because of thetight timing synchronization requirements between PUCCH on the PCell andPDSCH on the SCells, PCells and SCells can be assumed to be controlledby the same eNodeB.

For a given UE, the SCells may be activated or deactivated by MACsignalling. A terminal may be capable of uplink operation on two (ormore) carriers. Therefore in CA, uplink data on PUSCH, and BSR and someRACH can be transmitted by both PCell and SCell. For LTE up to andincluding Release 11 the uplink control channel (PUCCH), which supportsSR, is only transmitted on the PCell. Similarly, PRACH for requesting anUL resource allocation is only transmitted on PCell. PRACH may betransmitted on an SCell, but only for the purpose of determining timingadvance. However, these restrictions may not apply in future Releases.

One key scenario for the “Small Cell” concept, which is currently beingstudied in 3GPP, provides for the possibility of a terminal beingsupported by both a macro cell and one or more small cells, operating atthe same or different carrier frequencies. This has some similaritieswith CA, but the timing relation between the cells may be less strictlycontrolled for small cells, and the cells may be controlled by differenteNodeBs. It is likely that cells at significantly different frequencies(as envisaged for one of the small cells scenarios) would have differentchannel conditions and traffic capacities. The small cell carrier mayhave higher data rate capacity, but less consistent geographicalcoverage. In addition the backhaul capacity and latency may be differentfor macro cells and small cells. Therefore, under the Small Cell conceptit would be advantageous for the network to be able to control bothwhich data traffic from a given UE is routed via each carrier, and thearrangements for reporting uplink buffer status and scheduling requests,depending on channel conditions, which are likely to vary with time andlocation.

WO 2011/100673 A1 discloses a wireless communication method, wirelesscommunication network, terminal and base station according to thepreamble of each independent claim. When a terminal is connected withmultiple eNBs (sites) with one or more UL CCs to each site, one CC persite being defined as an anchor carrier, and one anchor carrier beingdefined as a primary CC, the corresponding UL anchor carrier associatedwith the eNB may be used for sending UL control information such asACK/NACK and channel state information. Alternatively, all UL controlinformation may be sent using the primary CC.

EP 2 391 172 A2 discloses a BSR scheme for a LTE MIMO system in which asingle eNB communicates with a UE, using either of the above mentionedBSR formats of FIGS. 6 and 7.

WO 2013/113390 A1 discloses a BSR scheme for a CA system in LTE in whicheither BSR is transmitted on both PCell and SCell in case both arescheduled, or alternatively the UE sends BSR on the allocated PUSCH asper Release-10 but with BSR cancellation on a CC basis, i.e. BSR for agiven serving cell is considered pending until is not transmitted on thecorresponding cell.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda wireless communication method wherein:

-   -   a terminal transmits first and second data streams to a network,        the network providing a plurality of cells serving the terminal;        characterised in that the first data stream is associated with a        both a first one and a second one of said cells, and the second        data stream is associated with a second one of said cells; and    -   the terminal transmits to the network at least one signalling        message including first information relating to data to be sent        in the first data stream and/or second information relating to        data to be sent in the second data stream.

Preferably, the terminal determines via which of the cells to send theat least one signalling message. In this case, the terminal may make thedetermination based at least on channel conditions with respect to eachcell.

In an embodiment, one such signalling message is transmitted via thefirst cell. Another such signalling message may be transmitted via thesecond cell.

On the other hand, two of the signalling messages may both betransmitted via the same cell.

The signalling messages in the present invention may take various forms.They may include a buffer status report, a scheduling request, or aPRACH signature.

Preferably each data stream is further associated with a logical channeland/or a logical channel group.

The association between a data stream and a cell may be changed bysignalling from the network to the terminal.

The first and second cells may be controlled by different base stations.

According to a second aspect of the present invention, there is provideda wireless communication network providing a plurality of cells servinga terminal, the terminal arranged to transmit first and second datastreams to the network, characterised in that the first data stream isassociated with a both a first one and a second one of said cells, andthe second data stream is associated with a second one of said cells;and

-   -   the terminal is further arranged to transmit to the network at        least one signalling message including first information        relating to data to be sent in the first data stream, and/or        second information relating to data to be sent in the second        data stream.

According to a third aspect of the present invention, there is provideda terminal in a wireless communication network, the network providing aplurality of cells serving the terminal, the terminal arranged totransmit first and second data streams to the network, characterised inthat

-   -   the first data stream is associated with a both a first one and        a second one of said cells, and the second data stream is        associated with a second one of said cells; and    -   the terminal is further arranged to transmit to the network at        least one signalling message including first information        relating to data to be sent in the first data stream, and/or        second information relating to data to be sent in the second        data stream.

According to a fourth aspect of the present invention, there is provideda base station providing at least one serving cell of a terminal havinga plurality of serving cells, the cells used by the terminal to transmitfirst and second data streams, characterised in that

-   -   the first data stream is associated with a both a first one and        a second one of said cells, and the second data stream is        associated with a second one of said cells; and    -   the base station is arranged to receive from the terminal at        least one signalling message including first information        relating to data to be sent in the first data streams, and/or        second information relating to data to be sent in the second        data stream.

In a further aspect, the present invention provides software in the formof computer-readable instructions which, when executed by a processor ofradio equipment, provides the base station or the terminal as definedabove. Such software may be recorded on one or more non-transitorystorage media.

The term “cell” in this specification is to be interpreted broadly. Forexample, it is possible to refer to communication channels associatedwith a cell being transmitted from or by the cell (in the downlink), ortransmitted to a cell (in the uplink), even if the transmission orreception is actually carried out by one or more antennas or antennaports of a base station. Whilst the term “cell” normally implies both adownlink and an uplink, this is not essential and in the presentinvention at least one cell may be an uplink-only cell. The term “cell”is intended also to include sub-cells, which could be sub-divisions of acell based on using particular antennas or corresponding to differentgeographical areas within a cell. References to performing certainactions “at a cell” generally implies performing those actions in a basestation which provides that cell.

The cells may be associated with different base stations or with thesame base station. The term “base station” itself has a broad meaningand encompasses, for example, an access point or transmission point. Theterms “network” and “system” are used interchangeably in thisspecification and intended to have an equivalent meaning, and the“E-UTRAN” of LTE is one possible network/system to which the presentinvention may be applied.

The radio bearer, apart from its specific meaning in the context of LTE,can be regarded as a service provided by the access stratum of thecellular wireless network to the non access stratum (core network) fordelivering data between a terminal and the core network.

The data streams, information on which is contained in the first andsecond signalling messages, comprise data in a buffer of the terminal,used to hold data temporarily prior to uplink transmission. In thepresent invention the signalling messages contain information on data tobe sent in the data streams, or more particularly information on logicalchannels associated with the data streams. A logical channel means someform of designation applied to data within a radio bearer, for examplefor the purpose of scheduling. Since the logical channels are associatedwith cells, this allows the buffer status to be reported separately foreach cell.

Thus, embodiments of the present invention provide for association ofdata streams (and/or logical channels) with individual carriers (cells),and independent buffer status reporting per carrier for terminals withmore than one uplink carrier configured. This is particularlyadvantageous in a “Small Cell” scenario for 3GPP LTE, where a terminalmay be simultaneously served by a macro cell and one or more smallcells. These may operate at different frequencies, have differenttraffic loading and support different QoS (Quality of Service).Embodiments may allow independent control of traffic on the uplinks tothe macro cell and the small cells, which can be used to optimize theuser experience in relation to the available resources at any giventime/location, and allows particular data to be routed via particularcells.

In general, and unless there is a clear intention to the contrary,features described with respect to one aspect of the invention may beapplied equally and in any combination to any other aspect, even if sucha combination is not explicitly mentioned or described herein.

As is evident from the foregoing, embodiments of the present inventioninvolve signal transmissions between cells and terminals (UEs) in awireless communication system. The cells are associated with one or morebase stations. A base station may take any form suitable fortransmitting and receiving such signals. It is envisaged that the basestations will typically take the form proposed for implementation in the3GPP LTE and 3GPP LTE-A groups of standards, and may therefore bedescribed as an eNodeB (eNodeB) (which term also embraces Home eNodeB)as appropriate in different situations. However, subject to thefunctional requirements of the invention, some or all base stations maytake any other form suitable for transmitting and receiving signals fromterminals.

Similarly, in the present invention, each terminal may take any formsuitable for transmitting and receiving signals from base stations. Forexample, the terminal may take the form of a user equipment (UE),subscriber station (SS), or a mobile station (MS), or any other suitablefixed-position or movable form. For the purpose of visualising theinvention, it may be convenient to imagine the terminal as a mobilehandset (and in many instances at least some of the terminals willcomprise mobile handsets), however no limitation whatsoever is to beimplied from this.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made, by way of example only, to the accompanying drawingsin which:

FIG. 1 shows a network topology in LTE;

FIG. 2 illustrates the principle of a Small Cell Network (SCN);

FIG. 3 illustrates channels at each of a plurality of protocol layers inLTE;

FIG. 4 shows how LTE physical channels are allocated to a PCell andSCell in a SCN;

FIG. 5 illustrates a protocol stack for the uplink of a wirelesscommunication system configured for carrier aggregation (CA);

FIGS. 6 and 7 show respectively a short-form and a long form BSRemployed in LTE;

FIG. 8 illustrates the conventional relationship between radio bearers,logical channels and cells in LTE;

FIG. 9 is a flowchart of steps in a method embodying the presentinvention;

FIG. 10 is a schematic block diagram of a terminal for use in thepresent invention; and

FIG. 11 is a schematic block diagram of a base station for use in thepresent invention.

DETAILED DESCRIPTION

The problem which led the inventors to conceive of the present inventionis that the current mechanisms in LTE for reporting uplink buffer statuswere designed under the assumption of a single uplink carrier forcontrol signalling, and single set of (semi-statically configured)logical channels for uplink data transmission. For the Small Cell casethis does not allow data (i.e. logical channels) to be easilydistinguished in terms of which uplink carrier would be most appropriatefor transmission, and does not allow buffer status reporting andscheduling requests to dynamically depend on which carriers arecurrently available.

For example, in a typical case a macro cell and a small cell would becontrolled by different eNodeBs, which may schedule uplink transmissionsindependently. In addition at least some uplink control signalling (e.g.UE initiated RRC signalling) is most appropriately sent to the relevanteNodeB. Similarly, if the macro cell and small cells provide differentlatencies, it would be appropriate to route data for applicationsrequiring low latency (e.g. VoIP) via the appropriate cell. Further, ifthe macro cell is relatively more heavily loaded, then low priority highvolume data should be routed via the small cell.

A principle of embodiments is to enable an association between a datastream (logical channel) and a cell (or more than one cells). Theinventors have realised that in LTE this can also be convenientlyrealised using the existing mapping of logical channels to logicalchannel groups, but providing a further mapping between logical channelgroups and cells. This mapping can be one to many (i.e. datacorresponding to a logical channel group can be transmitted on more thanone cell). It should be noted that conventionally there is no specifiedrelationship in LTE between LCs/LCGs on one hand, and carriers/cells onthe other hand.

FIG. 9 shows this principle in the form of a simplified flowchart. First(S10) it is determined which cells are currently available to (activatedor prepared for) the UE. In step S12, LCGs are assigned to the availablecells. As already mentioned this is not necessarily a one-to-onerelationship. In S14, data streams are assigned to logical channels andthe logical channels to LCGs. In step S16 the UE detects that there isdata waiting for transmission for a particular data stream, and in stepS18 it responds to this detection by sending a signalling message(BSR/SR/PRACH) to the network which message relates to the cell (orcells) associated with that data stream. This message may be sent on thecell associated with the data stream, but need not be. In S20, the UEreceives a scheduling grant on the relevant cell. Then in step S22 theUE uses the granted resources on that cell to send the waiting data ofthe data stream.

Having outlined a principle underlying some embodiments of the presentinvention, the embodiments themselves will now be described.

In general, unless otherwise indicated, the embodiments described beloware based on LTE, where the network (wireless communication system)comprises multiple eNodeBs, each controlling one or more downlink cells,each downlink cell having a corresponding uplink cell. Each DL cell mayserve one or more terminals (UEs) which may receive and decode signalstransmitted in that serving cell. In order to control the use oftransmission resources in time, frequency and spatial domains fortransmission to and from the UEs, the eNodeB sends control channelmessages (PDCCH or EPDCCH) to the UEs.

A PDCCH/EPDCCH message typically indicates whether the data transmissionwill be in the uplink (using PUSCH) or downlink (using PDSCH). Theresource assignments granted by the eNB in the DL are determined usingchannel state information. This is provided by feedback from the UEbased on channel measurements made using reference signals which may betransmitted by the eNB for each cell that it supports. This feedbacktypically consists of one or more instances of a data rate in the formof a channel quality indicator (CQI), a precoding matrix indicator (PMI)and rank indicator (RI). It is assumed that a UE is served by a macrocell and one or more small cells.

First Embodiment

In a first embodiment the macro cell and a small cell are eachcontrolled by a different eNodeB. It is determined that a particulardata stream (or streams) should be sent via a particular cell (e.g. UEinitiated uplink RRC signalling relating to the macro cell only via themacro cell, or low priority user data via the small cell).

Possible factors used for this determination include:

-   -   QoS of the data stream concerned    -   system bandwidth of cells    -   channel quality    -   traffic loading on the cells    -   latency available on the cells    -   power consumption at the UE when using a cell    -   financial cost of using a cell

Here, the bandwidth available on a given cell may be indicated to the UEby signalling. The channel quality with respect to a given cell may beestimated from the DL channel quality, or signalled from the basestation. The traffic loading on a given cell may be signalled by thebase station, or the UE may be able to estimate it. Latency is afunction of, among other things, the speed of a backhaul connectionbetween a base station and the rest of the network; it will generally behigher for a small cell (provided for example by a Home eNodeB orequivalent, connected to broadband internet) than for a macro cell(provided by a Macro eNodeB having dedicated links to the core network).Power consumption may vary for the UE depending on the carrierfrequency: other things being equal, a higher carrier frequency willraise the power consumption at the UE. The financial cost factor refersto the fact that a cell provided by a macro eNodeB will be subject to anormal usage/data tariff of a mobile operator, whilst a femtocell (orequivalent) might be free to use.

The above determination may be made either by the network, or by the UEwith guidance from the network. It will be noted that there is someoverlap among these factors; however, it may not be necessary toconsider all of the above factors. It may simplify the processingrequired to consider only the bandwidth for example. Another issue, whenthe UE makes the determination, is the information available to the UE:the UE may not know the channel quality or the traffic loading. In suchcases the bandwidth will give at least an indication to the UE of whichcell is a suitable one to carry the data stream.

More particularly, determining the association between data stream andcell may be by specification or network choice (e.g. RRC signalling),depending on the variation of the embodiment. For example thespecification may include a rule for determining which data stream is tobe transmitted via which cell, possibly expressed in terms of arelationship between radio bearers and LC/LCG. In any case, the variouscells which may be available to the UE can conveniently be labelled bythe cell ID, which is known to the UE.

Thus a data stream can be associated with a selected cell, and the datatransmitted using that cell. This association is achieved by assigning(or mapping) the data stream to a logical channel which is associatedwith the selected cell, and by assigning the logical channel to alogical channel group which is also associated with the selected cell.This is the same association for both LC and its LCG; in other wordsboth LC and LCG are associated with the same cell. The criteria forsending a BSR, SR or RACH are determined independently per cell,according to the logical channels assigned to that cell.

In a variation of the first embodiment, the assignment of logicalchannel groups is determined in dependence on which of the configuredcells are activated for the UE. It should be noted that “activated” inthis context means “capable of use by the specific UE”, rather thanoperational or not. For example, if the small cell is deactivated by MACsignalling, the mapping is changed such that all the logical channelgroups are mapped to the macro cell. In such a case, some logicalchannel groups may not be required. Incidentally, conventionally a givencell is activated for both uplink and downlink. However, independentactivation of a cell with respect to a UE's uplink or downlink may bepossible in future.

Different sets of logical channel groups may be configured for eachpossible combination of activated cells. In a given location, the set ofcells potentially available is known to the PCell eNodeB and configuredat the UE, and will normally be quite limited in number (with even fewercurrently activated for a given UE). Consequently it is possible tocalculate all possible combinations of cells. Reconfiguration could beperformed if a new cell becomes available (for example if a Home eNodeBis powered up).

In a further variation of the first embodiment, configurations for oneor more of BSR, SR and PRACH may be different for the macro and smallcell. There may be rules to define which cell is used for transmissionof these signals, or the UE may decide this, for example based onobservation of radio channel conditions (e.g. from measurements ondownlink reference symbols).

Two example of such rules are as follows.

(i) If a BSR is triggered due to arrival of data in a particular LC, ifthe LC is associated with a particular cell, the BSR is transmitted onthat cell if PUSCH resource is available in the current subframe. If noPUSCH resource is configured on that cell, then the BSR is transmittedon the cell with highest uplink channel quality for which PUSCHresources are available in the current subframe. If there are no PUSCHresources available on any cell, SR is triggered.

(ii) If an SR is triggered due to arrival of data in a particular LC, ifthe LC is associated with a particular cell, the SR is triggered on thatcell if a SR is configured, otherwise PRACH is transmitted on that cell.If the LC is not associated with a particular cell, and SR resources areconfigured on more than one cell, the SR is transmitted on the cell withthe highest uplink channel quality, or if no SR resources areconfigured, then PRACH is transmitted on the cell with the highestuplink channel quality.

Second Embodiment

A second embodiment is like the first embodiment, except that the cellsoperate according to carrier aggregation (CA), extended to allow SR (andPRACH for scheduling requests) to be transmitted on an SCell uplink. Asa variation, since the cells are controlled by the same eNodeB, there isless advantage in independent transmission of control signalling such asBSR via the different cells. Therefore a single BSR is defined to coverboth uplinks; in other words one signalling message contains individualstatus reports for two (or more) cells. This may be transmitted on PCellor (in contrast to current LTE specifications), on any SCell uplink.

Thus, this embodiment allows data streams to be preferentially routedvia particular cells, but only needs a single BSR which can cover thedata ready to send on both (or all) cells. The existing long-format BSR(FIG. 7) could be used for this purpose, with the fields representingdifferent LCGs and thereby indirectly, as a result of the mapping ofLC/LCG to cells, defining which cell(s) to use.

Third Embodiment

A third embodiment (which may be combined with the first and secondembodiments) includes a new type of BSR that is split into two parts;one part is the buffer status for UL data that may be transmitted byeither macro cell or small cell, and the second part is the bufferstatus for UL data intended for transmission by the small cell. Asalready mentioned, the mapping of LC/LCG to cell may be a one-to-manyrelationship such that a certain LCG can be associated with both cells.

In a variation of this embodiment the BSR report is split into threeparts. The additional third part is the buffer status for UL data notintended for transmission by the small cell. This may be achieved byconfiguring one LCG to map only to the PCell (macro cell). Each part maybe recognised by the respective relevant macro cell or small cell bymeans of a tag of one or two bits to signify which cell(s) the BSRapplies to; such a tag would also allow parts of the BSR to be sentindependently. This scheme would probably require defining an additionalBSR format to those of FIGS. 6 and 7.

A further variation of the above embodiment the BSR consists of multipledifferent parts that can be tagged differently for different smallcells. For example, using 2 bits, 4 different tags are available and aBSR could be transmitted in two parts, each with a 2-bit tag.

In variations of this embodiment the parts of the BSR transmitted may befixed in specification, determined by configuration or decided by theUE. If the UE has no data for a particular LCG, and the correspondingpart of the BSR is nevertheless to be transmitted, the UE would simplytransmit “0” (zero) in that part.

Fourth Embodiment

A fourth embodiment (which may also be combined with the first threeembodiments) does not in itself alter BSR reporting, but allows a changeof the cell handling a particular data stream by updating the associatedcell ID without changing other settings. For example it would bepossible to modify the DRB (data radio bearer) configuration withoutchanging other setting such as DRB-Identity, PDCP-Config, RLC-Config,logicalChannelIdentity and logicalChannelConfig. This may be based onthe channel condition in the cells involved for the UE.

In other words, this embodiment allows “renaming” a cell so that themappings of LCs/LCGs to cells take on a different meaning, and may leadto other changes such as a change of BSR format.

FIG. 10 is a block diagram illustrating an example of a UE 1 to whichthe present invention may be applied. The UE 1 may include any type ofdevice which may be used in a wireless communication system describedabove and may include cellular (or cell) phones (including smartphones),personal digital assistants (PDAs) with mobile communicationcapabilities, laptops or computer systems with mobile communicationcomponents, and/or any device that is operable to communicatewirelessly. The UE 1 includes transmitter/receiver unit(s) 804 connectedto at least one antenna 802 (together defining a communication unit) anda controller 806 having access to memory in the form of a storage medium808. The controller 806 may be, for example, Microprocessor, digitalsignal processor (DSP), application-specific integrated circuit (ASIC),field-programmable gate array (FPGA), or other logic circuitryprogrammed or otherwise configured to perform the various functionsdescribed above, such as determining the association between datastreams (or LCs) and cells in the manner outlined above. For example,the various functions described above may be embodied in the form of acomputer program stored in the storage medium 808 and executed by thecontroller 806. The transmission/reception unit 804 is arranged, undercontrol of the controller 806, to receive signals from the cells such asscheduling grants and so forth as discussed previously.

FIG. 11 is a block diagram illustrating an example of an eNodeB 11 towhich the present invention may be applied. The base station includestransmitter/receiver unit(s) 904 connected to at least one antenna 902(together defining a communication unit) and a controller 906. Thecontroller may be, for example, Microprocessor, DSP, ASIC, FPGA, orother logic circuitry programmed or otherwise configured to perform thevarious functions described above, such as determining the associationbetween data streams (or LCs) and cells when this is done on the networkside. For example, the various functions described above may be embodiedin the form of a computer program stored in the storage medium 908 andexecuted by the controller 906. The transmission/reception unit 904 isresponsible for transmission of configuration information, schedulinggrants and so on under control of the controller 906.

To summarise, embodiments of the present invention may provide forassociation of data streams (and/or logical channels) with individualcarriers (cells), and independent buffer status reporting per carrierfor terminals with more than one uplink carrier configured.

Various modifications are possible within the scope of the presentinvention.

As already mentioned, the term “cells” in the above description is to beinterpreted broadly. Cells need not each have a different geographicalarea, or a different base station. In general, cells can be defined on adownlink, uplink, or on both.

Conventionally, as explained above a UE obtains system information froma single PCell, but embodiments of the present invention are notrestricted to such an arrangement, and in future it may be possible toregard more than one cell as PCells of the same UE.

At least some of the embodiments described above may employ the existingBSR formats of FIGS. 6 and 7. Alternatively, new BSR formats may bedefined if preferred (for example to avoid confusion between existingand novel usages of LCG, where in the present invention the LCG impliesthe cell).

Normally, in a BSR, information on amounts (volumes) of data in the LCGsis conveyed. However, it is not essential to signify any absolute amountof data. Relative amounts of data among the LCGs and/or percentage filllevels of buffers are other possibilities.

Although in the above embodiments, the LCs are assigned to LCGs alongwith the step of assigning data streams to LCs, it is not essential toperform these steps at the same time. For example it may be possible toassign LCs to LCGs in advance of the step of assigning data streams toLCs.

The invention is equally applicable to LTE FDD and TDD, and theprinciple applied to other communications systems such as UMTS. If theinvention were to be included in 3GPP specifications for LTE it wouldprobably be in the following form:

-   -   in 3GPP TS 36.331, new RRC signalling to configure the        association between a logical channel group and cell; and    -   in 3GPP TS 36.321, new UE behaviour in relation to transmission        of BSR/SR/PRACH.

INDUSTRIAL APPLICABILITY

In a “Small Cell” scenario for 3GPP LTE, a terminal may besimultaneously served by a macro cell and one or more small cells. Thesemay operate at different frequencies, have different traffic loading andsupport different QoS (Quality of Service). By permitting independentbuffer status reporting per carrier for terminals with more than oneuplink carrier configured, the invention allows independent control oftraffic on the uplinks to the macro cell and the small cells, which canbe used to optimize the user experience in relation to the availableresources at any given time/location, and allows particular data to berouted via particular cells.

What is claimed is:
 1. A wireless communication method wherein: aterminal (1) transmits first and second data streams to a network;wherein the first data stream is associated with both a first cell and asecond cell of a plurality of cells (10, 20, 22, 24) serving theterminal, and the second data stream is associated with the second cell;and the terminal (1) transmits at least one signalling message includingfirst information relating to data to be sent in the first data streamand/or second information relating to data to be sent in the second datastream to at least one of the first cell and the second cell based onpredetermined rules corresponding to association between cells and datastreams.
 2. The method according to claim 1 wherein the predeterminedrules take into account data waiting for transmission in the first andsecond data streams.
 3. The method according to claim 1 wherein theterminal (1) determines via which of the cells (10, 20, 22, 24) to sendthe at least one signalling message.
 4. The method according to claim 3wherein the terminal (1) makes said determination based at least onchannel conditions with respect to each cell (10, 20, 22, 24).
 5. Themethod according to claim 1 wherein a said signalling message istransmitted via the first cell.
 6. The method according to claim 1wherein a said signalling message is transmitted via the second cell. 7.The method according to claim 1 wherein two signalling messages are bothtransmitted via the same cell.
 8. The method according to claim 1wherein the at least one signalling message includes a buffer statusreport.
 9. The method according to claim 1 wherein the at least onesignalling message includes a scheduling request.
 10. The methodaccording to claim 1 wherein the at least one signalling messageincludes a PRACH signature.
 11. The method according to claim 1 whereineach data stream is further associated with a logical channel and/or alogical channel group.
 12. The method according to claim 1 wherein theassociation between a data stream and a cell (10, 20, 22, 24) is changedby signalling from the network to the terminal (1).
 13. The methodaccording to claim 1 wherein the first and second cells are controlledby different base stations (11, 21).
 14. A wireless communicationnetwork providing a plurality of cells (10, 20, 22, 24) serving aterminal (1), the terminal arranged to transmit first and second datastreams to the network, wherein the first data stream is associated witha both a first cell and a second cell of said plurality of cells (10,20, 22, 24), and the second data stream is associated with the secondcell; and the terminal (1) is further arranged to transmit at least onesignalling message including first information relating to data to besent in the first data stream and/or second information relating to datato be sent in the second data stream to at least one of the first celland the second cell based on predetermined rules corresponding toassociation between cells and data streams.
 15. A terminal (1) in awireless communication network, the network providing a plurality ofcells (10, 20, 22, 24) serving the terminal, the terminal arranged totransmit first and second data streams to the network, wherein the firstdata stream is associated with a both a first cell and a second cell ofsaid plurality of cells (10, 20, 22, 24), and the second data stream isassociated with the second cell; and the terminal (1) is furtherarranged to transmit at least one/or signalling message including firstinformation relating to data to be sent in the first and second datastreams, and/or second information relating to data to be sent in thesecond data stream to at least one of the first cell and the second cellbased on predetermined rules corresponding to association between cellsand data streams.
 16. A base station (11, 21) providing at least oneserving cell of a terminal (1) having a plurality of serving cells (10,20, 22, 24), the cells used by the terminal (1) to transmit first andsecond data streams, wherein the first data stream is associated with aboth a first cell and a second cell of said plurality of cells (10, 20,22, 24), and the second data stream is associated with the second cell;and the base station (11, 21) is arranged to receive from the terminal(1) at least one signalling message including first information relatingto data to be sent in the first data stream, and/or second informationrelating to data to be sent in the second data stream, the signallingmessage transmitted to at least one of the first cell and the secondcell based on predetermined rules corresponding to association betweencells and data streams.